1. Introduction: The performance on Spitfire V.K.9788 (Merlin XLV engine) is given in 1st part of Report No. A.A.E.E./692,i.
It was desired to check the performance obtained on K.9788 on another Spitfire V. and X.4922 was chosen for these check tests.
Spitfire V. X.4922 was fitted with a standard Spitfire I. De Havilland airscrew, but with the pitch settings increased to 34° fine and 54 ° coarse, the same pitch settings used in the previous tests.

2. Tests made: The aeroplane was fitted with 8 Browning guns and, operationally equipped, weighed 6,450 lb.
Because this loading represented the all-up weight of the aeroplane in Service, it was decided to carry out the trials at the above load instead of 6,070 lb. to which K.9788 was loaded.
(Note: paragraph as corrected by corrigendum dated 18th June, 1941)

Climbs to ceiling and measurements of speeds over a range of heights from 10,000 feet to 26,000 feet were made.
An oil cooling climb was combined with the performance climb.

3. Results of tests:

(a) The top speed of the aeroplane is 375 m.p.h. at 20,800 feet.

(b) The maximum rate of climb is 3,140 feet per minute at 14,400 feet.
The time to 20,000 feet is 7.1 minutes and the Service ceiling is 37,700 feet.

(c) The radiator is not quite suitable for English summer conditions on the climb.

(d) The oil cooler is suitable for English summer conditions on the climb.

(e) The take-off run in zero wind and standard conditions is 330 yards,
and the distance to clear a 50 foot screen is 530 yards.

(f) The airscrew setting of 34 deg. to 54 deg. is suitable for the aeroplane under all conditions of flight.

4. Comments on results:

(a) The top speed of X.4922, 375 m.p.h. at 20,800 feet, is greater than Spitfire V K.9788 (364 m.p.h. at 19,600 feet).
The discrepancy is explained by the lower full throttle height of the Merlin XLV in K.9788 being 1,200 feet lower than that in X.4922.

(b) The maximum rate of climb of this aeroplane (3,140 feet/minute) is lower than that of Spitfire V. K.9788 (3,460 feet/minute).
However, the total all-up weight of X.4922 was 6,450 lb. compared with 6,170 lb., the all up weight of K.9788.

(c) The Mark II radiator in X.4922 seems to be less efficient than the Mark I. radiator on K.9788.
This discrepancy remains unexplained.

SUMMARY OF TRIALS

Aeroplane Spitfire V.

No. X.4922

Engine

Merlin XLV

At 2850 R.P.M.

and +9 lb. boost

At 3000 R.P.M.

and +9 lb. boost

Total weight =

6,450 lb.

C.G. position

6.2" aft of the datum

Heightfeet

TopSpeedM.P.H.

Time to Climb mins.

Rate ofClimbFt/min.

S.L.

0

2,000

0.7

2765

5,000

1.9

2855

10,000

337

3.6

3010

15,000

355

5.2

3045

20,000

372.5

7.1

2280

25,000

364.5

9.6

1520

30,000

12.9

1275

Service Ceiling

37,700 ft

Take off run

330 yds.

Distance from rest to clear 50 ft screen

530 yds.

Take off tests corrected to zero wind and standard atmosphere

CLIMBING TRIALS

HeightIn StandardAtmosphereFeet

TimeFromStartMin.

RateofClimbFt./Min.

TrueAirSpeedM.P.H.

A.S.I.M.P.H.

P.E.C.

Comp.

R.P.M.

Boostlb./sq.in.

Sea Level

0

.

.

.

.

.

2850

.

1,000

0.4

2735

171

170

-1.8

-

"

+9.0

2,000

0.7

2765

.

.

.

.

"

+9.0

3,000

1.2

2795

.

.

.

.

"

+9.0

5,000

1.9

2855

.

.

.

.

"

+9.0

6,500

2.4

2900

.

.

.

.

"

+9.0

10,000

3.6

3010

185

160

-0.4

-0.4

"

+9.0

13,000

4.6

3095

.

.

.

.

"

+9.0

15,000

5.2

3045

.

.

.

.

"

+8.6

16,500

5.7

2815

.

.

.

.

"

+7.6

18,000

6.2

2590

.

.

.

.

"

+6.5

20,000

7.1

2280

204

148

+1.5

-0.8

"

+5.2

23,000

8.7

1820

.

.

.

.

"

+3.2

26,000

10.2

1810

211

136

+3.5

-0.9

3000

+2.8

28,000

11.4

1540

214

132

+4.3

-1.0

"

+1.4

30,000

12.9

1275

216

128

+5.0

-1.0

"

+0.1

33,000

15.6

870

220

122

+6.3

-1.2

"

-1.8

36,000

20.2

470

225

116

+7.5

-1.1

"

-3.4

37,000

22.8

290

221.5

110

+8.7

-1.1

"

-3.8

14,400*

4.9

3140

193

155

*0.4

-0.6

2850

+9.0

Estimated absolute ceiling

38,000 feet

Greatest height reached

37,850

R.P.M. stationary on ground

2500

Boost pressure lb./sq.in

+8 3/4

* Full Throttle height

Service Ceiling. 37,850 ft.

SPEED TRIALS

HeightIn StandardAtmosphereFeet

TrueAirSpeedM.P.H.

A.S.I.M.P.H.

P.E.C.

Comp.

R.P.M.

Boostlb./sq. in.

10,000

337

300

-8.5

-2.4

3000

+9.0

13,000

347.5

296

-8.5

-3.2

"

+9.0

15,000

355

294

-8.5

-3.8

"

+9.0

16,500

360

291

-8.5

-4.2

"

+9.0

18,000

363

287

-8.5

-4.5

"

+9.0

20,000

372.5

285.5

-8.5

-5.2

"

+9.0

20,800*

375

276

-8.5

-5.8

"

+9.0

23,000

370

270.5

-8.5

-5.5

"

+6.6

26,000

361.5

252

-8.5

-5.5

"

+4.2

Landing and take off tests corrected to zero wind and standard atmosphere